Three new butanolides, (2E,3R,4R,9’Z)-2-(dodec-9’-en-11’-ynylidene)-3-hydroxy-4-methylbutanolid e (1), (2E,3R,4R)-2-(dodeca-9’,1 1’-diynylidene)-3-hydroxy-4-methylbutanolide(2),(2E,3R,4R,9’E)-2-(dodeca -9’,11’-dienylidene)-3-hydroxy-4-methylbutanolide (3) and one new ring-opened butanolide, methyl (2Z,11Z,1’R,2’R)-2-(1’,2’-dihydroxypropyl) tetradeca-2,11-dien-13-ynoate (4) were isolated from the leaves of the three representative species of the endemic primitive genus Hortonia (Monimiaceae), namely H. angustifolia, H. floribunda and H. ovalifolia. Their structures were elucidated on the basis of spectroscopic evidence.